Secret Letters

Teaching set

Observed lessons

When simple codes are not enough, use letters.

Divide the letters so no one letter gives full information.

Do not let messengers know the content of what they carry.

Discussion

Secret tallies are symbols that
represent a limited number of key messages that the reader will understand.
Sometimes you need to send more complex or non-standard messages, in which case
you will need to resort to words. The problem with words is that, if captured,
they can be read. Even if written in code, the code may yet be cracked.

A simple way of sending text that cannot be understood is to break the letter
into pieces and send each by a different route. Even if one part is intercepted,
the whole message cannot be read. The more parts the message is broken into, the
harder it will be to glean any information from each one.

In modern times, a typical use for this is to send a login user name and
password by separate email messages.